JavaScript 在 Canvas 2D 平面绘制数字 8 的算法解析

radian = angle/180 * Math.PI;

var x = Math.sin(radian);
var y = Math.cos(radian);

if(angle%720 > 360){
 y = -y+2;
}

<!doctype html>
<html>
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
 <meta http-equiv="X-UA-Compatible" content="ie=edge">
 <title>实现一个点在二维平面上面画8</title>
 <style>
  #canvas{
   display: block;
   margin:0 auto;
  }
 </style>
</head>
<body>
<canvas id="canvas" width="300" height="600"></canvas>
</body>
<script>
var canvas = document.querySelector("#canvas");
var ctx = canvas.getContext("2d");
var angle = 0; //角度
var radian = 0; //弧度
function draw() {
 angle += 2;
 radian = angle/180 * Math.PI;
 var x = Math.sin(radian);
 var y = Math.cos(radian);

 if(angle%720 > 360){
  y = -y+2;
 }

 var left = x*150+150;
 var top = y*150+150;

 ctx.arc(left, top, 1, 0, Math.PI*2);

 ctx.strokeStyle = "green";

 ctx.stroke();

 requestAnimationFrame(draw);
}

requestAnimationFrame(draw);
</script>
</html>